The present invention relates to a firing apparatus for a gas generator of a restraint device in a vehicle, a firing chamber filled with a pyrotechnic material being present; and a semiconductor chip, in which in addition to a firing resistor at least one circuit activating the latter is integrated, being arranged outside the firing chamber in such a way that during a firing operation, thermal energy generated by the firing resistor is transferred to the pyrotechnic material in the firing chambers.
A firing apparatus is known, for example, from German Patent No. 198 06 915 or WO 99/02937. The firing apparatuses described in these two documents aim not only to accommodate therein a pyrotechnic charge and a firing resistor responsible for the firing thereof, but additionally to accommodate circuit elements necessary for activation of the firing resistor as well as circuits for supplying energy to and/or diagnosing the firing apparatus. What is achieved thereby is a very compact, intelligent firing apparatus that can be connected, for example together with several other firing elements arranged at various points in the vehicle, to a common bus line which creates a connection to a central control unit. Each of the firing elements is installed, in known fashion, in a gas generator that, in the event of initiation, inflates an airbag or triggers a belt tightener.
In the firing apparatus described in WO 99/02937, several semiconductor chips are stacked one above another and contacted to one another using flip-chip technology. The semiconductor chip that is located closest to the firing chamber filled with the pyrotechnic material is embodied as a firing resistor which, when current flows through it, generates thermal energy and thus fires the pyrotechnic charge. A concrete arrangement of the semiconductor chip with the firing resistor and the firing chamber such that the thermal energy proceeding from the firing resistor is transferred to the pyrotechnic charge in the firing chamber, is not disclosed by WO 99/02937.
In German Patent No. 198 06 915, a firing resistor is integrated on a semiconductor chip, and a funnel having a pyrotechnic material charged thereinto rests directly on the semiconductor chip, so that the pyrotechnic material in the funnel is directly in contact with the firing resistor.
If the firing apparatus, as already stated, is connected along with other firing apparatuses to a common bus line, a signal transfer over the bus line to other firing apparatuses should still be possible even when a firing apparatus has already been activated. To ensure, in particular in the context of a daisy-chain bus concept, that signal transfer over the bus linexe2x80x94for the initiation of further restraint means or for a multi-stage initiation of restraint meansxe2x80x94is possible even after firing of a firing apparatus, the circuit in the activated firing apparatus should not be completely destroyed, but rather should continue to permit transmission of signals onto the bus line. It is therefore an object of the present invention to provide a firing apparatus whose circuit means remain undestroyed to the greatest possible extent upon firing.
According to the present invention, the semiconductor chip equipped with the firing resistor is retained on a circuit board; the circuit board is retained, with the side opposite the semiconductor chip, on a wall of the firing chamber; and an opening is present in the wall of the firing chamber and in the circuit board, so that a passage exists between the firing resistor mounted on the semiconductor chip and the pyrotechnic material in the firing chamber.
The firing chamber wall and the circuit board between the firing chamber and the semiconductor chip protect the semiconductor chip from the high temperatures and pressures occurring upon firing of the pyrotechnic charge in the firing chamber, so that the semiconductor, on which several circuit elements are integrated, is largely protected from destruction upon firing of the pyrotechnic charge. If a daisy-chain bus system is in use for the actuators of the restraint systems in the vehicle, signal transmission over the bus would be maintained if the electrical circuit of an activated firing apparatus having the features presented above were still at least partially functional, so that further firing apparatuses on the bus line can subsequently also be activated.
The semiconductor chip is preferably contacted to the circuit board using flip-chip technology, and a filler material is introduced between the circuit board and the semiconductor chip. This ensures optimal protection of the semiconductor chip from high temperature and high pressure during a firing operation.
It is advisable if a ridge surrounding the opening in the circuit board is arranged between the semiconductor chip and the circuit board. This ridge is a barrier to the filler material between the semiconductor chip and the circuit board, and furthermore forms a delimitation, with respect to the remaining region of the semiconductor chip equipped with the further circuit elements, of the combustion chamber in which the firing resistor is located. The ridge is preferably made of a solder material.
For the purpose of enhanced helium sealing, the opening in the circuit board can be equipped with a metallization, and a respective ring of solder material can be introduced both between the semiconductor chip and the metallization and between the wall of the firing chamber and the metallization.
It is advisable to solder the circuit board onto the wall of the firing chamber. A solder join is necessary so that helium sealing of the firing chamber is achieved.
The filler material between the circuit board and the semiconductor chip can be a capillary liquid adhesive or an adhesive paste.
To ensure that the firing delay between the firing resistor and the pyrotechnic charge in the firing chamber is as short as possible, it is advisable to introduce into the opening of the firing chamber wall a flammable contact material, having pyrotechnic properties, that is connected to the pyrotechnic material in the firing chamber.